Hello, SFIA audio listeners, in this month's Nebula exclusive, big alien theory,

we're asking the reason alien civilizations might be rare is because most aliens are huge.

To hear it and every episode early and ad-free, plus hours of bonus content,

check out go.nebola.tv slash Isaac Arthur and use my code, Isaac Arthur.

Welcome to the Upward Bound Series.

It's been about two and a half years since this series began in March of 2017 with

Gideon to Space, and at the time of this writing, it contains about 20 episodes,

looking at everything from rockets and space planes, to launch megastructures,

like the Orbiter Ring, to some of the things we might do in orbit or on the moon,

like beaming energy home or farming in space. In truth though, the series is a bit older than

that. During our first year, we began the megastructure series with looks specifically at some

of those large structures, like the space elevator, skyhooks, and space towers.

But this was early in the show, when not only was the audiovisual production very lacking,

but I'd taken the common advice of doing episodes shorter.

Our first four episodes were all well over half an hour long, and everybody knew you weren't

supposed to do videos that long, or no one would watch them.

Channel regulars know our typical episode these days is usually about 30 minutes, but for

a little while in that first year of 2015, I went way shorter, doing a few episodes that were only

about 10 minutes long, or even Skyhooks, our record shortest episode that wasn't a channel

trailer at a mere five minutes.

I soon decided that regardless of if that advice about going short was good advice,

it wasn't me and it wasn't the channel, and though I experimented briefly

...